Current control



Oct. 17,1933. H. A. WHEELER CURRENT CONTROL .Original Filed July 7, 1927 ATTORNEYS Patented Oct. 17, 1933 PATENT OFFICE CURRENT CONTROL Harold A. Wheeler, Great Neck, N. Y., `assignor to Hazeltine Corporation, a corporation of.Dela- Ware Original application July 7, 1927, Serial No. 203,879. Divided and this application May 22,

1931. July 3, 1928 2 Claims.

This invention relates to electric current control and more particularly to the regulation of current through any of a plurality of seriesconnected impedances while still maintaining 5 the current through the other impedances substantially constant.

This application is a division of my copending original application Serial No. 203,879, filed July 7, 1927.

This invention has particular application to vacuum tube operation. In accordance with the arrangement herein described there is provided an arrangement for enabling the current through any of a plurality of series connected vacuum tube filaments or heating elements to be varied without producing an appreciable variation of the current through the `remaining filaments.

It is common practice to control the volume output of a radio receiver by regulating the current through the filament or heating element of one or more of the vacuum tubes of the receiver. Furthermore, it is often convenient to arrange the filaments or heating elements in series with the source of heating current. In such an arrangement, a common method of regulating the current through one of the filaments is to shunt across that filament a variable resistance. Such an arrangement satisfactorily varies the current through the filament with which the Variable resistance is associated, but it also Varies the current through the remaining filaments to a certain degree.

In accordance with this invention a variable resistance is shunted across the filament or heating element of the tube or tubes which are to be regulated and also another variable resistance is inserted in the series circuit. A single controlling element simultaneously operates both variable resistances in such a manner that when one resistance is increased the other is correspondingly decreased. The result is that the current supplied to the regulated tube is varied while the current through the series circuit remains substantially constant.

The single figure of the drawing is identical to Fig. 7 of my said original application Serial No. 203,879.

The drawing illustrates a radio receiver which includes an antenna 56 connected by means of a transformer 57 to a neutralized three-stage tuned radio-frequency cascade amplifier including vacuum tubes 58, 60 and 62 coupled one to the next by transformers 59 and 61. The last stage of the amplifier is coupled through a Serial No. 539,319, and in Great Britain transformer 63 to the input of a detector tube 64, which input circuit includes a fixed condenser 55. The transformers 59, 6l and 63 are provided with neutralizing windings between which and the grids of the associated tubes, are connected neutralizing condensers 52, 53 and 54. The secondary windings of transformers 57, 59,

61 and 63 are shunted, respectively, by variable tuning condensers C1, Cz, C3 and C4.

The detector, or rectifier tube employed may 65 be of the type commonly known in the art as a two-electrode Fleming valve, or may consist of an equivalent such as a three-electrode vacuum tube, as shown, having its grid and plate directly connected together to comprise in effect a single anode 66. The output circuit of the rectifier tube includes a resistance 65 which is connected between the anode 66 and the filament 67 of the rectifier. A resistance 72 and condenser 68 associated with this output 75 circuit, constitutes a rejector network which filters out the radio-frequency current component in the output circuit of the rectifier, while the network including a condenser 69 and a resistance 70 constitutes an audio-frequency- 80 pass filter for coupling the output circuit of the rectifier to the input circuit of an audio-frequency amplifier comprising amplifying tubes 71 and 77 and 79. An audio-frequency transformer 76, which is preferably of a low ratio of trans- 35 formation, couples the output circuit of vacuum tube 71 to the second audio-frequency amplifying tube 77. The second audio-frequency tube is in turn coupled by a second audio-frequency transformer 78 to the third audio-frequency tube 90 '79, in the output circuit of which there is included a loud speaker 80.

Automatic amplification control is effected in this receiver in a manner explained in detail in the original application No. 203.879. Briefly, the automatic volume control circuit comprises a resistance 82 and a connection 88. One end of resistance 82 is connected to a point in the output circuit of the detector between resistance 72 and condenser 69, and the other end is con- 10o nected through connection 88 and resistances 83 and 85 to the grids 84 and 86, respectively, of radio-frequency amplifier tubes 58 and 60.

Impedance 82 and the condenser 87 constitute an audio-frequency-stop filter, so that substantially only direct voltage is impressed upon the grids 84 and 86.

Signals received at the antenna are amplified in the radio-frequency amplifier, rectified by the rectifier 64 and successively amplified at 110 an audio-frequency by the vacuum tubes 71, 77 and '79. The rectified current in the output circuit of' the rectifier fiows through the resistance 65 and thereby develops a negative voltage at the terminal 81, which voltage is applied through the impedances 72, 82, 83 and 85 to the grids 84 and 86 of amplifying tubes 58 and 60 respectively. The amplification of the tubes 58 and 60 is simultaneously controlled by means of the negative bias applied to their respective grids by the direct current component of the rectified output of the detector. Thus a strong signal received at the antenna will tend to produce a large rectified current and hence small amplification; and a weak signal will tend to produce a smaller rectified current and hence a large amplification. The result is that the signal intensity impressed upon the detector remains substantially uniform over a wide range of received signal intensities.

To complete the description of the system illustrated, certain design data or constants are given herewith. It should be understood, however, that these as Well as all oth^r constants appearing in the present specification are mentioned simply by way of example in describing certain specific embodiments which in practice, have proved eminently satisfactory; and are not intended to suggest any specific limitations as to the scope of this invention.

Accordingly, fixed condenser 55 may be of .0005 microfarads capacity; condenser 68, .0001 microfarads; condenser 87, .O1 microfarads; condenser 69, .005 microfarads; resistance 65 of 1 megohm; resistance 72, 1 megohm; resistances '70, 82, 83 and 85, 2 megohms each; and the grid condensers connected at the junction of resistances 83 and 85 and the grid electrodes 84 and 86 may each be .001 microfarads.

The power supply for the receiver is a source of rectified and filtered alternating current which furnishes the filament potential A, plate potential B and also a source C of grid bias voltage for tube 79. The grid of tube 77 is biased by connecting the grid return lead to an appropriate point in the series filament circuit, as shown.

The variable tuning condensers C1-C4 are grounded in order to limit undesirable capacity effects as well as to make it practicable to conlnect the condensers on a single shaft for unicontrol operation, if desired. The power supply system is grounded, thus eliminating the danger of short-circuiting the direct-current supply when a separate ground is necessary for the alternating current rectifying and filtering system.

Assuming that the vacuum tubes employed are of the type having five-volt filaments, 35 volts of filament, or A, supply is needed. As above mentioned, the automatic volume control is here applied to two tubes, namely 58 and 60; the cut-off being effected with the use of two different plate, or B voltages. The anode 66 of rectifier 64 is more negative relatively to the filament of tube 58 than relative to the filament of tube 60, by the five-volt drop across one filament. To compensate for this difference, 35- volts higher B voltage is applied to the plate of tube 58, than to the plate of tube 60 which makes both tubes cut-off practically at the same time.

In addition to the combined advantages just outlined, the arrangement of the receiver also includes an additional feature which has not previously been described, namely, the means 130 for determining the filament current supplied to one of the amplifying tubes. This means is a compound rheostat comprising three resistances R11, R1 and R2, the former of which is fixed and the latter two, variable. Resistances Ru and R1 are joined in series and connected in shunt with the filament 74 of tube 7l, the resistance of which is designated by Rf. Variable resistance R2 is connected in series with the parallel arrangement of filament 74 and resistances R11 and R1. The connection between R1 and R2 is an electrical conducting arm 89 which connects the variable contacts of R1 and R2. The arm 89 is adjustable in such a manner that movement of the arm causes the magnitudes of resistances R1 and R2 to vary simultaneously in opposite directions.

When operating the filaments of the several vacuum tubes on rectified and filtered current from an alternating current power source, it is desirable that the filaments be connected in series since it is at present more practicable to provide a current supply at a comparatively high Voltage and low current.

It has previously been indicated that a common method of controlling the filament current through one of the tubes such as '71, is to provide a shunt rheostat in parallel with the filament of the tube so that the current divides between the rheostat and the filament. While the shunt rheostat means for controlling the filament emission of a single tube is fairly satisfactory, the arrangement of the device 130 is a substantial improvement. With the simple shunt rheostat method, an increase in current through the controlled filament is accompanied by a smaller decrease in current through the other filaments in series.` The improved arrangement shown in the drawing, on the other hand, by providing three resistances, two of which are simultaneously variable allows a variation of the voltage on one or more filaments Without affecting the current through the other filaments; or more generally, without changing the load on the filament current supply. It is apparent that benefits from this device will be especially manifested in an arrangement such as the present, wherein the current supply for the filaments is obtained from a rectified, filtered alternating current source, particularly when the rectifyig device is of the common type without automatic voltage regulation.

It mayhere be pointed out that while the drawing illustrates the manual control of the filament of only one tube, namely filament 74, the filaments of the other tubes could be connected either in series or in parallel with filament 74, if it be desired that independent simultaneous control be had of more than one filament. Rf may therefore be taken to represent the effective resistance of the filaments to be controlled. When the two resistances R1 and R2 and the fixed resistance R11 are properly proportioned to the normal operating resistance Rf of the filament or filaments of the tubes to be controlled, the resistance of the system as a whole will remain substantially constant during adjustment of the controlled device 130. By

way of example, the following data are given,

Rif-20 ohms, R0 will equal 20 ohms, R1 will equal 160 ohms, and R2, 10 ohms.

Although the control system has been described particularly with reference to vacuum tube filaments or heating elements, it could be applied equally well to arrangements of other types of impedances or resistances.

I claim:

1. In combination, a plurality of impedances connected in series with a source of current and a device for varying the current through a rst of said impedances and simultaneously maintaining the current through the other impedances constant, said device comprising a pair of resistances, an adjustable contact connected. to each of said resistances and a control for simultaneously adjusting said contacts, one terminal' of a rst of said resistances being connected to one terminal of said rst impedance and the contact of said first resistance being connected to the other terminal of said first impedance, and the portion of said second resistance between the. adjustable contact and another point being connected in series with said impedances and said source, said contactsbeing movable between the terminals of said resistances. y

2. In a system of a plurality of impedance elements connected in series with a source of current, means for controlling the current through certain of said elements, while maintaining substantially constant the current through the remainder of said elements, said means comprising a variable resistance connected in series with said plurality of impedance elements and with said current source, a variable resistance connected in shunt with said certain elements, and a mechanical control device for simultaneously /varying said resistances in such a manner that one resistance increases in magnitude at the same time that the other resistance decreases in magnitude.

HAROLD A. WHEELER. 

